Calculation of time delay Δ t per distance r

Time difference and sound path (distance or length)

Conversion: Delay time to milliseconds or microseconds ←→ sound path to meters, cm, feet or inches
The acoustic time of the travelling sound is converted to distance , or the length is converted to time
A time interval Δ t - even period of time, or time period - is more or less an extensive portion of the time period.
Distance r    Speed (velocity) c = r / Δ t

Notice: 1 second (s) = 1000 milliseconds (ms) and 0.001 second (s) = 1 millisecond (ms).
1 millisecond (ms) = 1000 microseconds (µs).

 Time difference (delay) Δ t in milli-   seconds (ms) or microseconds (µs) ms  µs |  |  | Distance r in meters (m), centi-   meters (cm), feet (ft), or inches ('') m  cm  ft   '' | ↓ |   | ↓ | Distance r m | Time difference (delay) Δ t s cm | = seconds s ft | + milliseconds ms '' | + microseconds µs For speed of sound c = m/s  ft/s
 Fill in the gray fields above, select the unit and click on the calculation button of the respective column. Also the adjusted speed of sound c can be changed: 343 m/s or 1125.33 ft/s at 20°C. When converting seconds to distance, the seconds have to be multiplied by 1000 and entered in the first field with the unit ms. The well known maximum value of the time difference (ITD) from ear to ear is 0.63 ms – and the strange "ear distance" that is believed to be 0.175 m = 17.5 cm. Really? Do a calculation.        c = r / Δ t        r = Δ t × c        Δ t = r / c        r = distance

 Using the formula Δ t = r / c shows that the propagation of sound over a distance r in meters (m) is always connected to a time t in seconds (s). For example this correlation is important when calculating a delay line and using the Haas effect. Distance = time × velocity.

In SI units with dry air at 20 °C (68 °F), the speed of sound c is 343 m/s.
This also equates to 1235 km/h, 767 mph, and 1125 ft/s.

The time duration of sound per meter (in air)

Effect of temperature on the time difference Δ t
Dependence of the speed of sound only on the temperature of the air

 Temperature  of air in °C Speed of sound c in m/s Time per 1 m  Δ t in ms/m +40 354.9 2.818 +35 352.0 2.840 +30 349.1 2.864 +25 346.2 2.888 +20 343.2 2.912 +15 340.3 2.937 +10 337.3 2.963 +5 334.3 2.990 ±0 331.3 3.017 −5 328.2 3.044 −10 325.2 3.073 −15 322.0 3.103 −20 318.8 3.134 −25 315.7 3.165

 Sound engineers take usually the rule of thumb:  For the distance of r = 1 m the sound needs about t = 3 ms in air.   Δ t = r / c and r = Δ t · c     Speed of sound  c = 343 m/s at 20°C,  equivalent to rounded 3 ms/m.

Temperature Dependence of Physical Quantities

Comb filter, Time delay Δ t and sound path r